I choose both. State parks generally provide a more serene setting. Sites are larger and more private. Camping rates are generally cheaper.
Private campgrounds provide more amenities,pools,exercise rooms etc.. Sites while smaller may have concrete pads and landscaping. Roads maybe paved FHU sites are generally available vs. no sewers in state parks.
Why limit yourself to one or the other. Choose best value based on your needs.
Sometimes a pool or full hook up site is desirable. While some places a larger private site is best.
There is no just right answer. There are very nice state and private parks available pick the best option in your area. It's always nice to have options/choices.